1. Field of the Invention
The present invention relates to a wheel structure and relates more particularly to an auxiliary wheel structure for attaching to the wheel frame of a folding hand truck at the back, which can be pulled out to match with the wheels of the folding hand truck to which it is attached for stair climbing operation, or pushed back into an idle position.
2. Description of Prior Art
Various types of hand trucks have been disclosed for moving heavy loads. A hand truck to which the present invention pertains generally comprises a L-shaped frame body having a wheel frame with wheels controlled by a handle to move a shelf to carry loads. The L-shaped frame body may be made in a folding structure so that it can be folded up into a collapsed arrangement to reduce space occupation when it is not in use. This type of folding hand truck is very helpful to travelers, more particularly to those commercial travelers. This structure of folding hand truck is very practical for use to move heavy loads on a smooth ground, however, it is not satisfactory in use for stair climbing operation. While passing through a stepped ground surface or climbing over stairs, a hand truck may be caused to overturn and the loads thereon may drop here and there. Further, this structure of folding hand cart is equipped with one pair of wheels transversely aligned. Therefore, it must be held in position by the hand after loading. Releasing of hands from the handle of a hand truck after loading immediately causes a hand truck to overturn.